The present invention relates to enclosures for electronic components and more specifically, to a method and apparatus for reducing flame emissions from such enclosures.
Electronic enclosures often include a plurality of fans for cooling electronic components mounted on printed circuit boards within such enclosures. The fans draw air into the enclosure at an air inlet port and cause the air to travel along an air flow path to an air exhaust port where the air exits the enclosure. The printed circuit boards are disposed in the air flow path and the components are cooled as the air flows across the boards.
In the event of a failure, it is possible for a circuit board to malfunction in such a manner as to ignite a fire on the malfunctioning board. The flames from the fire are fanned by the airflow produced from the fans and may exit the enclosure at the air exhaust port. Flames exiting the enclosure can ignite secondary fires and cause substantial damage. For this reason, it is important to minimize the emission of flames from electronics enclosures.
The Network Equipment Building System (NEBS) standard has been promulgated governing flame emissions from electronic network equipment enclosures. Section 4.2.2.1 of the NEBS GR-63-CORE requirements specifies, inter alia, that visible flames shall not extend beyond the horizontal or vertical confines of the equipment under test for 30 seconds or more. Compliance with this standard is tested by igniting a fire on a circuit board within the air flow path and determining whether flames extend beyond the enclosure for longer than the prescribed period. In practice compliance with this standard has proved difficult.
Various techniques for minimizing flame emissions from electronics enclosures have been employed. Baffles have been employed in an effort to redirect the flames. The use of baffles, however, undesirably increases back pressure and decreases cooling efficiency. In another approach to the solution of this problem, the amount of air permitted to enter the enclosure has been reduced by reducing the opening sizes at the air inlet or exhaust ports. These approaches also undesirably reduce the cooling efficiency. Additionally, none of the above described techniques adequately reduced flame emissions from the enclosure in a reliable manner so as to permit compliance with the aforementioned standard.
It would therefore be desirable to have a method and apparatus which minimized flame emissions from electronic cabinetry to reduce the risk of the ignition of secondary fires in the vicinity of such cabinetry.